stop-double-post.user.js

// ==UserScript==
// @include  *love2d.org/forums/viewtopic.php*
// ==/UserScript==
(function(){
function getElementsByTagAndClass(tag, cls) {
	var tags = document.getElementsByTagName(tag);
	var ret = [];
	for (var i = 0; i < tags.length; ++i) {
		if (tags[i].className.indexOf(cls) > -1)
			ret.push(tags[i]);
	}
	return ret;
}

// get own name
var logoutStr = getElementsByTagAndClass("li", "icon-logout")[0];
var user = logoutStr.firstChild.title.replace(/^Logout \[\s+/, "").replace(/\s+\]$/, "");

// get author list
var posts = getElementsByTagAndClass("div", "post ");
var authors = []
for (var i = 0; i < posts.length; ++i) {
	var author = posts[i].childNodes[1].childNodes[2].childNodes[5].childNodes[2].firstChild.innerHTML; // yeah, i know...
	authors.push(author);
}
var beforebeforelast = authors[authors.length - 3];
var beforelast = authors[authors.length - 2];
var last = authors[authors.length - 1];
function checkDoublePost() {
	if (last == user) {
		if (beforelast == user) {
			if (beforebeforelast == user) {
				alert("Quadruplepost?! NO!");
				return false;
			}
			return confirm("Triple post? Really?");
		}
		return confirm("Are you sure you want to double post?\nYou can always edit your post.");
	}
	return true;
}

// add question popup to reply and quote links
var links = [];
var reply = getElementsByTagAndClass("div", "reply-icon");
for (var i = 0; i < reply.length; ++i)
	links.push(reply[i].firstChild);

var quote = getElementsByTagAndClass("li", "quote-icon");
for (var i = 0; i < quote.length; ++i)
	links.push(quote[i].firstChild);

for (var i = 0; i < links.length; ++i)
	links[i].onclick = checkDoublePost;
})();